1. Field of the Invention
The present invention relates in general to methods of cleaning semiconductor production equipment, and relates in particular to a cleaning method for a chemical vapor deposition chamber for depositing a thin film of a ferroelectric or highly dielectric material, such as barium/strontium titanate, on a semiconductor substrate.
2. Description of the Related Art
In recent years, there has been a quantum jump in circuit density of integrated circuit devices produced by the semiconductor industries, and intense development activities are underway in anticipation of giga-bit order DRAMs replacing the prevailing mega-bit order DRAMs of today. Dielectric thin film materials used to make high capacitance devices necessary for producing DRAMs have, in the past, included silicon oxide or silicon nitride films of dielectric constant less than ten, tantalum pentaoxide (Ta.sub.2 O.sub.5) films of dielectric constant of about twenty; metal oxide films of dielectric constant of about three hundred, such as barium titanate (BaTiO.sub.3) or strontium titanate (SrTiO.sub.3) films, or barium/strontium titanate films of a mixed composition, appear to be promising.
To deposit a thin film of such a high dielectric constant material on a substrate, a chemical vapor deposition apparatus is used in which one or more gaseous feeds of organo-metallic compounds and an oxygen containing gas are supplied onto a substrate heated to a certain constant temperature.
In such an apparatus, reaction products produced during the film deposition process are adhered to the inside surfaces of the deposition chamber, causing problems of degradation in product quality and hindering of the process of stable deposition. It is therefore necessary to periodically remove (clean) such reaction products accumulated inside the chamber. Cleaning operation has traditionally been performed by opening and exposing the apparatus to air atmosphere, and cleaning the apparatus physically or chemically.
However, cleaning in air atmosphere means that the apparatus must be shut down to break the vacuum inside the chamber, and restarted to restore deposition conditions, so that the process is not only time-consuming but results in loss of operating efficiency.
A cleaning method based on plasma etching using a halogen gas has also been proposed for silicon oxide deposition apparatus. A plasma is generated in the deposition chamber by introducing a halogen gas (e.g. SF.sub.6) into the chamber for producing halogen radicals to react with the reaction products adhering to the inside wall of the chamber, thereby to produce gaseous halogen compounds which will be easily exhausted by a subsequent evacuation process.
However, such a cleaning method based on plasma etching cannot be applied to deposition apparatus for making high capacity memories made of highly dielectric thin film materials, because the resulting halogen compounds are not volatile, and therefore the reaction products are left unaffected in the deposition chamber.